This invention relates to floating roofs for covering liquid products, such as petroleum products and the like, in large storage tanks, and wherein the roof floats on the stored liquid product. Such roofs typically comprise a substantially flat, planar deck and an annular pontoon secured to a peripheral portion of the deck and seal means engaged between the roof and an inner side wall surface of the tank. Another typical construction comprises a substantially flat, planar deck having an upstanding peripheral rim thereon and seal means engaged between the rim and an inner side wall surface of the tank, said roof floating as a shallow pan on the liquid stored in the tank. It is desirable, regardless of the structure of the roof, that the deck be in substantially complete contact with the stored liquid product to prevent accumulation of vapors and also to prevent contamination of the stored liquid. Also, it is desirable to provide some means operatively connected with the deck, such that in the event of leakage of stored liquid onto the upper surface of the deck, sinking of the roof is eliminated and uneven settling of the deck is minimized. For example, some tanks may approach or exceed 300 feet in diameter, and if liquid product leaks onto the upper surface of the deck in these tanks, the deck may sag at the center up to 40 inches, and this may result in permanent deformation or damage to the floating roof structure. Also, floating roofs of the pan type could sink into the stored liquid and settle to the bottom of the tank if the stored liquid leaks onto the upper surface thereof.
Various attempts have been made in the prior art to solve the above problems, and several such approaches have utilized the attachment of a plurality of separate buoys or buoy units to the deck, such that if stored liquid leaks onto the upper surface of the deck, the buoys displace the leaked liquid and impart buoyancy to the roof to float the roof and prevent sinking or uneven settling thereof into the stored product. However, in all such prior art constructions the buoy units are not completely uniformly and even spaced apart on the surface of the deck, and in fact, in some prior art arrangements the buoys radiate much like spokes of a wheel, thus defining large pockets in which leaked product could accummulate, and also leaving relatively large expanses of the deck unsupported. Other such arrangements utilize a plurality of separate and independent buoy units secured to the deck, wherein if lines were drawn between the centers of adjacent buoys, rectangular configurations would be formed, or in other words, the buoy units are arranged in repeating rectangular grid arrangements on the deck. However, this type construction requires the use of a large number of buoy units and there is relatively uneven support for some portions of the deck. For example, in one such typical construction the distance between adjacent buoys in one direction may be between 18 and 19 feet, and the distance between adjacent buoys in a direction perpendicular to the first direction may be on the order of 22 or 23 feet.
In accordance with the present invention, a plurality of spaced apart, separate and independent buoy units are secured to the deck of a floating roof and extend upwardly therefrom, and the buoy units are arranged such that lines drawn between the centers of any three mutually adjacent buoys form a substantially equilateral triangle. Thus, with the present invention any given buoy is permitted to support more deck area than prior art devices, meaning that a fewer number of buoys can be employed to support a given roof. Also, the substantially equilateral triangular spacing between adjacent buoys results in a more even distribution of the load on the deck, and a resultant generally lower state of stress in the deck. Further, the deflection of the deck between adjacent buoys is lower in magnitude than prior art structures, with the result that a given load is supported in a more uniform manner. Also, the buoys or buoy units located adjacent the periphery of the deck are more evenly distributed when compared with prior art structures.